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Simulations of Adsorptions and Phase Transitions

Shi, Wei (2003) Simulations of Adsorptions and Phase Transitions. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The objective of this thesis is to developsimulation tools that will allow us to study many phenomena from amolecular level. The topics covered inthis thesis include bulk phasetransitions, phase transitions in adsorbed fluids,and the application of single-walled carbon nanotubes as a gasstorage media.Multiple histogram reweighting and mixed-field finite-size scaling techniqueshave been developed to calculate the phase diagram for classical andquantum fluids in bulk and adsorbed phases.We show, for the firsttime, that capillary condensation showsa crossover of the effectiveexponent for the width of the coexistence curve from 2-DIsing-like (1/8) farther away from the critical point tomean-field (1/2) near the critical point.The first prewetting transitions clearlyobserved from simulation of quantum fluids are presented.The experimentalwetting temperature of 19.1 K is reproduced from the simulationwith a modified potential. Hydrogen adsorbing on a 15 AA thickfilm of Rb on Au gives a wetting temperatureof about 1 K less than H$_2$ on pure Rb.This prediction should be observablefrom experiments.Hydrogen adsorption onto single walled carbonnanotube bundles has been performed from computer simulationsand compared with the experiments. We studythe effect of CO$_2$ oxidation of the nanotubes on adsorption. Isothermscomputed with a standard graphitic potential giveremarkably good agreement with the experimentally measured isotherms beforeactivation with CO$_{2}$. The effect of activation is modeled byindependently increasing the nanotube spacing and the solid-fluidinteraction potential. It is found that onlya combination of increased nanotube spacing and increased solid-fluidpotential gives rough agreement with experiments.Gases such as CH$_4$, Xe, and Arhave been studied on both the homogeneous (same tubediameter) and heterogeneous (different tube diameters)closed single-walled carbon nanotube bundles constructed fromthe basin-hopping method.Experimental gas adsorption data on SWNT bundles have previously been analyzedin terms of an over-simplified model of homogeneous nanotubespacked into perfect arrays. This analysis has led to the generalconclusion that gases do not adsorb inside interstitial channelsof homogeneous nanotube bundles.Our analysis overturns the current paradigm of gas adsorption onSWNTs by showing that adsorption inside interstices ofheterogeneous SWNT bundles isvitally important to accurately describing these materials.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Shi, Weiweishi@pitt.eduWEISHI
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairJohnson, J Karlkarlj@pitt.eduKARLJ
Committee MemberBockrath, Bradley
Committee MemberBorguet, Ericborguet@pitt.eduBORGUET
Committee MemberHolder, GeraldHolder@engr.pitt.eduGDHVMS
Committee MemberEnick, Robertenick@engr.pitt.eduRME
Date: 3 September 2003
Date Type: Completion
Defense Date: 5 May 2003
Approval Date: 3 September 2003
Submission Date: 7 May 2003
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Chemical Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Simulation Adsorption Phase transition hydrogen ca
Other ID:, etd-05072003-013447
Date Deposited: 10 Nov 2011 19:43
Last Modified: 15 Nov 2016 13:43


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